Radio coverage information is important in network planning, network optimization, optimization of radio resource management (Radio Resource Management: RRM) parameters and the like (Non Patent Literature 1) and a drive-test is performed by an operator in order to detect coverage problems within a network, such as a coverage hole, pilot pollution and the like. In the 3GPP (3rd Generation Partnership Project), in order to reduce operation expenditure (OPEX) incurred in a drive-test by an operator, utilization of a radio terminal (User Equipment: UE) for measurement and report of such information that has been collected by the drive-test or information similar thereto is under study (Non Patent Literature 1).
<MDT>
An ultimate object of the abovementioned study is the minimization of execution of the drive-tests (Minimization of Drive-Tests: abbreviated as “MDT”). In the MDT studies, the following are being discussed:
how a radio terminal is made to perform measurement, and
how a radio terminal is made to report a log of results of measurement or of past measurement results; where “measurement” includes not only measurement of channel quality, but also operations of “detecting” a certain specific situation, such as a radio coverage problem.
A radio network to which a radio terminal (UE) makes a report includes an (E-)UTRAN base station ((e)Node B), or an UTRAN base station control station (Radio Network Controller: RNC), or the like. An E-UTRAN base station eNB includes some functions of an RNC that manages radio resources and a base station NodeB that terminates a radio interface in an UTRAN. An E-UTRAN eNodeB or an UTRAN NodeB and RNC are denoted as “eNB/RNC” in the present specification.
(E-)UTRAN: (Evolved-)UMTS (Universal Mobile Telecommunications System) Terrestrial radio Access Network)
eNode B: evolved Node B (eNB)
<Logged MDT>
At present (at the time of filing the present application), in one measurement mode specified in the specification of Non Patent Literature 2, there is a method (Logged MDT) in which a radio terminal (UE) is made to perform measurement while in an idle mode and is made to report a measurement result to a radio network while in an active mode. In the following, as a premise for understanding of the present invention, an outline of Logged MDT is described, based on the specification of Non Patent Literature 2 and the like.
The idle mode is a power supply ON mode such as when the radio terminal (UE) is in a standby mode or the like, and is referred to as a mode in which an RRC (Radio Resource Control) connection is not established (Non Patent Literature 8). The idle mode indicates RRC_IDLE (Radio Resource Control IDLE) in LTE (Long Term Evolution) and UTRAN IDLE in UMTS (Universal Mobile Telecommunications System). When the radio terminal (UE) is in the idle mode, management as to in which serving cell the radio terminal (UE) is, is not performed. In LTE, management is performed as to in which Tracking Area (TA) the radio terminal (UE) camps (the TA is managed by an MME (Mobility Management Entity) or the like), and in UMTS, management is performed as to in which Location Area (LA) or Routing Area (RA) the radio terminal (UE) camps (the LA or RA is managed by an MSC (Mobile Switching Center)/VLR (Visitor Location Register)). It is to be noted that that in 3GPP, UMTS a CELL_PCH or URA_PCH state may be considered a target for a Logged MDT. The following describes Logged MDT focusing on an idle mode, but the basic situation is similar also for CELL_PCH or URA_PCH.
A radio base station/base station control station (eNB/RNC) of an (E-)UTRAN instructs a radio terminal (UE) in an active mode to execute measurement in an idle mode and to record measurement results (logging). That is, the radio base station/base station control station (eNB/RNC) of an (E-)UTRAN transmits an Idle MDT configuration message including a configuration parameter of a Logged MDT executed by a radio terminal (UE) in an idle mode to the radio terminal (UE) (Non Patent Literature 2). (This is a general term for UMTS/LTE, and in case of focusing on LTE, may be also called “Idle Logging Configuration message”).
After transitioning from an active mode to an idle mode, the radio terminal (UE) executes measurement and logging in the idle mode, in accordance with an instruction from the (E-)UTRAN. Here, a cell that is a target for measurement is basically the same as a UE in a normal idle mode. That is, measurement in a Logged MDT follows the principle of measurement in an idle mode of a radio terminal (UE) (Non Patent Literature 4, 5).
Basically, a target for measurement is:
a cell included in a neighboring cell list,
a cell besides a neighboring cell list and detected by a UE (a detected cell).
A non measurement target is:
a cell in a black list,
a CSG (Closed Subscriber Group) cell when “PCI/PSC split” is applied to distinguish a CSG cell and an Open cell, by physical cell identification information (PCI/PSC) (applicable to a radio terminal (UE) that is a non CSG member, not having functionality/authority belonging to a CSG cell).
It is to be noted that the black list is a list of cells that is used to prevent the radio terminal from performing measurement (quality measurement) of a specific neighboring cell in the list.
A CSG cell restricts connections to a radio terminal (UE) of a specific group, such as the owner of a femto base station (Femto (e)NB or Home (e)NB) or its family, for example.
Therefore, an open cell is a cell that all UEs of an operator can use, only specific radio terminals (UEs) can use CSG, and a hybrid cells is a mixture of open and CSG cells.
<Coverage Hole>
It is under study that in case of a radio terminal (UE) being camped in a coverage hole, the radio terminal (UE) performs logging as “Out Of Service” (OOS) (outside of operation area), instead of logging measurement results of a serving cell or neighboring cell (Non Patent Literature 3).
On the other hand, it is also under study that in case of a radio terminal (UE) being camped in a coverage hole, the radio terminal (UE) continues MDT measurement and Logging only in a specific time-period (for example, while a terminal is in a “camped normally” state) and suspends MDT measurement and Logging, in case of the radio terminal remaining camped in a coverage hole even after the specific time period has elapsed (for example, while the terminal is in an “any cell selection” or “camped on any cell” state) (Non Patent Literature 2). In a case where when the radio terminal returns again to a “camped normally” state, an Idle MDT Configuration is valid, the radio terminal restarts MDT measurement and Logging.
Here, a coverage hole is an area in which SNR (Signal to Noise Ratio) or SINR (Signal to Interference and Noise Ratio) of a serving cell or a neighboring cell for which serving (connection, also referred to as “establishment of a radio link”) is allowed in order to perform a predetermined service, is less than a preset value necessary for maintaining basic service (establishing an SRB (Signaling radio Bearer), and acquiring information to be sent by DL common channels (downlink common channels)). Here, the SRB is a bearer for carrying an RRC (Radio Resource Control) message, which is a control message.
As to a point in time when a radio terminal (UE) determines a coverage hole, the following may be cited as examples:
a case where it is not possible to select a cell in which the radio terminal (UE) is allowed to be served in order to perform a predetermined service during when the radio terminal (UE) is in a “camped normally” state (broadcast (or paging) information could not be acquired),
a case where it is not possible to select a cell in which the radio terminal (UE) is allowed to be served during when the radio terminal (UE) is in an “any cell selection” state,
a case where it is not possible to select a cell in which the radio terminal (UE) is allowed to be served in order to perform a predetermined service during when the radio terminal (UE) is in a “camped on any cell” state.
In the present specification, it is assumed as an example that a coverage hole is determined in a case where it is not possible to select a cell in which a radio terminal (UE) is allowed to be served in order to perform a predetermined service during when the radio terminal (UE) is in a “camped normally” state.<Allowed Cell/Radio Base Station>
A cell/radio base station in which a terminal is allowed to establish a radio link with the radio base station for performing a predetermined service, is called an allowed cell/radio base station in the present specification. Conversely, a cell/radio base station in which a terminal is not allowed to establish a radio link with the radio base station for performing a predetermined service, but is allowed to be served only for receiving a restricted service, and/or, a cell/radio base station in which a terminal is inhibited from being served, is called a “not allowed cell/radio base station” in the present specification. The latter, for example, corresponds to a CSG cell for a non-member.
A radio terminal (UE) for which a Logged MDT is configured performs measurement in an idle mode, notifies an (E-)UTRAN that the radio terminal (UE) holds a log, at a point in time when the radio terminal (UE) goes into an active mode and establishes an RRC connection, and responsive to an instruction to report the log from the (E-)UTRAN, makes a report.
A radio terminal (UE), which is made from a radio network side to execute MDT measurement and logging in an idle mode, by using 1 bit in a connection complete (RRC_CONNECTION Setup Complete) message, for example, at a time of establishment of an RRC connection in a transition to an RRC_CONNECTED state in LTE, gives an indication to the radio network side that an MDT measurement result is available. The radio network retrieves a log of the measurement results based on the indication. For example, a radio base station (eNodeB: eNB) of the E-UTRAN transmits a UE Information Request to the radio terminal (UE) in order to perform log retrieval (collection) and the radio terminal (UE) reports a log of the measurement results as a UE Information Response.
Thus, it is possible for an (e)NodeB/RNC or an upper level network server (Core Network: abbreviated as “CN”, or Operation Administration and Maintenance: abbreviated as “OAM”) to comprehend a coverage problem. Retrieving a log(measurement result) held by a radio terminal (UE) from the network, and reporting the held log(measurement result) from the radio terminal is termed as log retrieval (collection), in the present specification.
Below, an LTE system is assumed, and using FIG. 22, an example of operations of a radio terminal (UE) is given.
The radio terminal (UE) that receives an instruction to execute periodic measurement of a Logged MDT, from an eNodeB in LTE, goes into an idle mode (RRC_IDLE) at time t=t0. At this time the radio terminal (UE) is assumed to camp in cell 1.
At time t=t0, the radio terminal (UE) performs logging of measurement results (RSRP and/or RSRQ) of serving cell 1 and neighboring cell 2.
At t=t1, the radio terminal (UE) cannot select a connectable cell during a preset time-period, and detects a coverage hole and suspends measurement. Thereafter, while in a state where a connectable cell cannot be selected, instead of a measurement result, logging of “OOS” (out of service) may be performed. In a case where it is possible to select cell 1 once again or another connectable cell, the radio terminal (UE) restarts MDT measurement.
The radio terminal (UE) moves to cell 2 in an idle mode, and at t=t2, performs logging of measurement results of cell 2 (serving cell) and neighboring cell 1.
At t=t3, the radio terminal (UE) goes into an active mode (RRC_CONNECTED), and reports the log retained by the radio terminal (UE) to the base station eNodeB2 of cell 2.
Thus, in a case where the UE detects a coverage hole, by reporting received quality until the coverage hole is detected or the fact (OOS) that there is a coverage hole to the eNodeB, it is possible to execute a required solution such as coverage optimization, based on the relevant fact, by the eNodeB or an upper level network server such as the OAM.
[NPL 1]
    3GPP TR36.805 v9.0.0    (Internet <http://www.3gpp.org/ftp/Specs/html-info/36805.htm>)[NPL 2]    R2-105238 (3GPP TS37.320 v1.0.0 (2010-08))    (Internet <http://www.3gpp.org/ftp/tsg_ran/WG2_RL2/TSGR2_71/Docs/R2-105238.zip>)[NPL 3]    R2-103942    (Internet <http://www.3gpp.org/ftp/tsg_ran/WG2_RL2/TSGR2_70bis/Docs/R2-103942.zip>[NPL 4]    3GPP TS25.133 v4.0.0 (2001-03)    (Internet <http://www.3gpp.org/ftp/Specs/archive/25_series/25.133/25133-400.zip>)[NPL 5]    3GPP TS36.133 V9.4.0 (2010-06)    (Internet <http://www.3gpp.org/ftp/Specs/archive/36_series/36.133/36133-940.zip>)[NPL 6]    3GPP TS36.304 v9.3.0    (Internet <http://www.3gpp.org/ftp/Specs/html-info/36304.htm>)[NPL 7]    3GPP TS36.300 v9.4.0    (Internet <http://www.3gpp.org/ftp/Specs/html-info/36300.htm>)[NPL 8]    3GPP TS21.905 v9.4.0    (Internet <http://www.3gpp.org/ftp/Specs/html-info/21905.htm>)